- Grandmaster Galaxy Master Quest - The first hack of a 3D Mario game listed here. Also the first Galaxy 2 hack ever made.
- Binary City, a Battle City hack except you control 2 tanks at the same time. Now a 4-directional action shooter has been turned into a puzzle game which requires a lot of thinking power, a lot of muscle coordination and a quick reflexes to win.
- Lots of Super Metroid hacks are hard for the casual player, requiring tricks that only advanced players learn... but some hacks go the extra mile and are hard even for experts. Super Metroid Impossible, the various RBO hacks, and the original version of Cliffhanger are notoriously difficult.
- Median XL, a Diablo II mod which gives you a wide selection of new skills and powers for your character and has several "uberquests" that contain monsters which can instantly pwn your player character, even at max level with good gear. Also veteran monsters in the normal game are instant pwn. Some areas have witches which cannot be killed or targeted by your character, but if you get within their awareness radius, they will instantly kill your character (guaranteed, cannot be resisted and damage is infinite).
- Brotherhood of Shadow for Knights of the Old Republic. Beautiful storyline, excellent characters, and holy Yoda, what an epic scope. But the difficulty level is brutal. Especially the one-on-one duel with Mandalore the Indomitable where you are armed with an unmodified lightsaber and robes and he's armed with a pair of battleaxes! He's also got a Force resistance of "yes."
- The Tomb of Jesset Dal'Kest is worse. Specialized armor and weapons on everything you fight, no party member backup, and boss-level characters attacking in a Zerg Rush. Even the mod's authors admit that it's world-class brutal.
- Populous: Age of Chaos was an unofficial expansion for Populous: The Beginning which introduced a brand-new, 25-level, single-player campaign that was far, FAR more difficult than both the original campaign and the one from the official expansion, Undiscovered Worlds, for veteran players who had beaten those two campaigns.
- Similar to the Super Metroid example above, ROM hacks of Super Mario World are often ridiculously difficult to the point of parody.
- Final Fantasy Tactics wasn't the hardest game out there, despite a few truly grueling battles... So some people gathered together and created Final Fantasy Tactics 1.3, which removed many exploits, rebalanced classes and gave enemies ridiculously powerful items and classes way before you can attain such things (unless you steal and use Mediators, of course)
- The Destination Paris mod for Commandos 2 cranks the difficulty of a series already renowned for being Nintendo Hard as it is Up to Eleven. It adds more enemies to missions, makes them more ruthless, adds freezing cold to some missions that will kill your men without arctic gear (a feature in the main game, though only in one level) and takes away the Bottomless Magazines from the pistol. The final mission is particularly brutal, as if you don't react very very quickly, your men will all be spotted and killed within less than a minute.
- The RTS/FPS/Vehicle Combat game, BattleZone II, has the Fleshstorm 2 mod - a mod which is brutally difficult. One mission requires you to escort a large, slow, unarmed tracked vehicle (your mobile base) through narrow passes while the planet's atmosphere is on fire. The armor of your tank, your Assault Tank, and the mobile base are constantly being whittled down from the heat of the air, so you must constantly keep at least one of your units repaired by your shielded Service Truck. The canyons you're driving through are also dotted with enemies, so there's a delicate balancing act between repairing all your support units, repairing yourself, and repairing the mobile base. Several times during the mission, you have to move ahead to take out targets so the base can pass by safely - meaning you need to leave the protection of your service truck's repair laser. If you go too far out, you'll die before you can make it back to the service truck. If you take too much damage, you'll die before you make it back to the service truck. And unlike the other missions, you cannot eject, as your pilot will die almost instantly under the heat.
- Pokémon Vega, a Japanese hack of Pokémon Fire Red, makes grinding a painfully time consuming affair by lowering the levels of all trainers and wild Pokémon down to as low as 10 or 15 fewer than the gym leader and evil team administrators' teams. It's necessary, though, since the major trainers come out swinging from the get go and never let up. By the third gym you'll have run into a Starmie with near flawless type coverage, a Kappa-like Pokémon with typically late game moves like Surf and Aura Sphere, and a ground type gym leader sending out a Hitmonchan as his clutch, all likely 5 or six levels higher than your strongest 'mon, unless you went out of your way to grind enough for them.
- Pokémon Blaze Black 2 & Volt White 2, a hack for Pokémon Black 2 & White 2. If played in the "Challenge Mode" (which you can acesses in the beginning of the game), the difficulty will become absolutely brutal. ALL gym learders have six pokémon, most (if not all) holding items (some which you can only get by half of the game onwards), likely three or five levels higher than your team, not to mention the great type coverage and strategies they possess. So you want to use fire attacks against the bug type gym leader? First thing he will do is use Rain Dance (which will make fire attacks 50% weaker) combined with Damp Rock item (extending the Rain Dance duration to eight turns instead of five). Good luck with that!
- Pokemon Crystal Enhanced is a game specifically made to be as hard as possible. For example, where Falkner has a Pidgey and a Pidgeotto around level 10 in the original, in this game, Falkner has a Skarmory, Aerodactyl, Gligar, and Mantine around level 17. And once you get to the post game, the gym leaders have no problems pulling out legendaries that surpass the level limit, and with Red the Pokemon can be up to level 165! And the creator made it to be nuzlocked too!
- There are plenty of mods out there for Baldurs Gate 2 to increase the difficulty of the bosses and make enemies behave more intelligently. Most notable among them, however, are two mods:
- The Tactics mod. For an example, the De'Arnise Keep dungeon is suddenly filled with Spirit Trolls, which you don't even encounter until halfway through the game, and even then only one at a time, and as for Tor'Gal, the boss of the dungeon (keep in mind that this is one of the very first dungeons you can go to):
- Has Improved Invisibility cast on him, preventing him from being able to be targeted by single-target spells.
- Can berserk himself
- Has Free Action cast on him, preventing any spells that restrict his movement from working
- Is immune to fear
- Automatically detects invisible characters
- Drains his target's strength with every hit
- Has an insanely high Healing Factor
- Carries one of the heads of the Flail of Ages (the perfect anti-troll weapon), meaning you can't forge the best weapon for clearing this dungeon until it's too late.
- Ascension, which beefs up all of the major boss fights in Throne of Bhaal (including Demogorgon,) and turns the final boss fight into a massive Boss Rush against every major villain from both the main game and To B (including fighting every member of the Five at the same time.) The only consolation is that you can recruit one of the Five to fight alongside you.
- The So Cool It's Awesome Empire at War mod Republic at War tweaks the enemy AI to be absurdly intelligent and ruthlessly aggressive.
- The Legend of Zelda: Parallel Worlds may be So Cool It's Awesome, but it is also one of the hardest games you will ever play. After beating the game you'll probably think all of the quotes on this trope's quote page are referring to this game specifically. One needs only look at level 3, Farore's Isle, for an example: After a couple of non-challenging rooms (literally a couple!), you're faced with an unavoidable Firebar that you'll absolutely have to take a hit off of to get by. And you'll probably want at least three hearts, because the room after that has more Firebars and red Hardhat Beetles that deal two hearts of Collision Damage at a time. And the next floor down has more red Hardhat Beetles and the Crystal Switch you have to activate to continue further on. And you'll need at least two hearts left over after going through all of that, because on the way back you'll be forced to hit a Firebar again! And you can't use the book of Mudora to go back to the start of the dungeon, because that resets the crystal switch! And hey, guess how much the remodel (specifically designed to make the game easier) changed about this series of rooms? Besides brightening them up a bit, absolutely nothing!!
- Mega Man 8-Bit Deathmatch's single player campaign is composed of a series of pre-determined matches against computer controlled bots. However, each level requires you to reach the frag limit to finish in first place, and the bots are very aggressive, and while it's possible to lower their difficulty, it's hard to access and not avaliable in the main single player menunote . Worse yet, they get infinite ammo for any weapon they pickup, allowing them to fire off weapons all day that would normally only have 7 shots at the most. And then some of the single player exclusive bosses battles are brutal, such as the Metool Daddy, and as the player cannot respawn during these fights, you have to start the fight over if you die at any point.
- Hideous Destructor is a weapon/gameplay mod for Doom that makes it play like a tactical shooter. A tactical shooter with Doom-like numbers of enemies who are at least as fast and tough as you are. If you get damaged you can bleed to death over time if you don't have the right items, you move at a realistic speed that is agonizingly slow compared to the Sonic-like speed of the original player character, and all enemies do tremendous amounts of damage. It's a truly harrowing experience and there is no room for mistakes.
- While it's still in Beta, the Advanced Arsenal Pack for Brutal Doom turns an already tough mod into a nightmare, since now the lowly zombiemen can carry rocket launchers, which they never drop as pickups. If you want your own launcher to level the playing field, you gotta find one laying around.
- The later parts of The Adventures Of Massmouth, as well as its sequel, Massmouth 2. The enemies aren't numerous, but they have a lot of health and hit really hard, all while ammo is very scarce.
- The Dwarf Fortress mod "Dig Deeper" is designed for people who have gotten the hang of regular DF and want a fresh challenge. And by "fresh challenge" we mean "endless tide of Orcsnote before your first caravan".
- Hacks of Yoshi's Island tend to be nearly impossible in terms of difficulty, often because they mix Artoon's love of instant kill spikes and lava with the original game's tendency to have absolutely gigantic puzzle levels. Just watch any one raocow has played for examples.